Use of a hardenable copper alloy for molds

ABSTRACT

The invention relates to use of a hardenable copper alloy containing 0.1% to 0.5% beryllium and 0.5% to 2% nickel for the production of broad side plates for thin slab continuous casting molds at casting speeds of at least 2 to 6 m/min and higher.

[0001] The invention relates to the use of a hardenable copper alloy formolds, in particular, for production of broad side plates for thin slabcontinuous casting molds.

[0002] At the present state of the art, the mold broad plates for thinslab plants and, in particular, for CSP (Compact Strip Production)plants are produced from copper alloys such as CuCrZr(copper-chromium-zirconium) or CuAg (copper-argentum). At that, the CuAgalloy for CSP-mold plates proved to be advantageous because of itscomparatively high elongation at elevated temperatures.

[0003] However, mold broad plates of CuAg or CuCrZr are not capable towithstand high thermal stresses prevailing in the region of the bathlevel of the molten metal, and have a tendency to form cracks in theplates in this region, with the CuCrZr having a tendency to aparticularly earlier crack formation. This crack formation is a primaryfailure criterium for the mold broad plates and results in high repairand replacement costs incurable by an operator of a continuous castingplant.

[0004] It should be noted that CuAg, despite its reduced tensilestrength, has a reduced crack formation tendency because, as a result ofits increased extensibility at high temperatures in the mold plate, itis capable of absorbing stresses and because its comparatively high heatconductance permits to retain smaller mean operational temperature.

[0005] For narrow side plates of thin slab molds, at the present stateof the art, usually, CuCrZr with a hardness of about 125 HB is used,with their side contact surfaces being nickel-plated for increasinghardness.

[0006] The primary failure criterium of the narrow side plates, indistinction from the broad side plates, is not the crack formation butrather wear or abrasion of contact surfaces by steel. Contrary to this,the primary failure criterium of the broad side plates is the crackformation in the molten level region.

[0007] German Patent DE 31 20 987 C2 discloses a number ofprecipitation-hardenable copper alloys and their use for stationarycontinuous casting molds, among others, different CuNiBe-alloys whichcontain other alloying components niobium (Nb), zirconium (Zr),magnesium (Mg), and/or titanium (Ti).

[0008] U.S. Pat. No. 2,137,281 discloses a copper alloy CuZrNiBe for astrip mold (twin-belt casting) characterized by a combination offeatures of a comparatively high heat conductance.

[0009] British Patent No. 954,796 discloses a copper alloy CuBeZrTi formolds which, at a comparatively good heat conductance, has comparativelyhigh strength values.

[0010] For a disturbance-free casting operation, in particular, for thinslabs with high speeds, e.g., of 6 m/min and more, the existingmechanical characteristics of mold materials are not adequate forcontrolling occurring high temperatures, in particular, in the region ofthe bath level.

[0011] Proceeding from the above-mentioned state-of-the-art, the objectof the invention is to provide suitable copper alloys for producingbroad side plates for thin slab continuous casting molds at high speeds,the use of which, during a casting operation, would prevent a prematurecrack formation, in particular, in the region of the molten level, andthe wear of contact surfaces by the fluid steel, and which wouldwithstand, at a lasting service life, extremely high thermal andmechanical loads during a casting operation.

[0012] The object of invention is achieved by use of a hardenable copperalloy with content of beryllium from 0.1% to 0.5%, content of nickelfrom 0.5% to 2.0% (CuNiBe) for production of broad side plates for slabcontinuous casting molds.

[0013] Advantageously, this copper alloy, after being hardened, iscapable of withstanding high thermal stresses in the bath level region,with reduction in crack formation, while being available over largeroperational time periods.

[0014] In addition to this successful operational result, contrary tothe known copper alloy such as CuCrZr or CuAg, the inventive copperalloy CuNiBe permits to achieve advantageous material characteristics,e.g., a substantially higher tensile strength of about 770 or about650^(N)/mm² and, at a 0.2 proof stress, of about 500^(N)/mm² both at 20°C. and at 300° C. The material characteristics of three selected, by wayof example, copper alloys CuCrZr, CuAg, an CuNiBe are given in thefollowing tables:

Material Characteristics

[0015] MATERIAL CHARACTERISTICS CuAg CuNiBe Approximate CuCrZr Cold-Specially Values Content Hardened Formed Hardened Chemical CompositionChemical % .70 Cr  .09 Ag 1.8 Ni Composition % .10 Zr .006 P .30 BePhysical Characteristics Heat W/mk  340 370 300 Conductance MechanicalCharacteristics RT at .2 proof N/mm² 300 265 500  20° Stress Rp .2Tensile N/mm² 415 3880 770 Strength Rm Elongation A5 % 25 18 15 RT at .2proof N/mm² 240 195 420 300° Stress Rp. 2 Tensile N/mm² 330 200 650Strength Rm Elongation A5 % 18 10 8 RT at Hardness HB 125 100  20° C.

[0016] Other positive characteristics, e.g., resistance to mechanicalwear follow from the high harness of the inventive material of about 220HB, because CuNiBe has approximately the same hardness as a galvanicallyapplied nickel layer having approximately 220-230 HB. The broad sideplates need not any more be nickel-plated.

[0017] The lower, in comparison with CuAg heat conductance of about 370W/mk, heat conductance of the copper alloy CuNiBe of about 300 W/mk canbe compensated by water-cooling of reduced copper wall thickness byabout 25%.

[0018] The inventive copper alloy CuNiBe for production of broad sideplates for thin slab continuous casting molds with high casting speeds,e.g., from 2 to 6 m/min contains as alloy components 0.1% to 0.5%beryllium, 0.5% to 2% nickel, and copper up to 99.5% by weight.

[0019] It should contain not more than 0.5% of impurities under which,e.g., traces of other metals such as Fe, Zr, Ag, Cr, Mg., etc. . . . areunderstood.

[0020] The invention provides for use of not obvious from thestate-of-the-art, special copper alloy CuNiBe for broad side plates ofcontinuous casting molds which enables casting of thin slabs with highspeeds of at least 2 to 6 m/min and more. The noticeable improvement ofoperational characteristics due to the extended service life, inparticular, a reduced crack formation in bath level region, economicaluse of material, and low-cost manufacture are results of the particularselection of the alloying components.

1. Use of a hardenable copper alloy with content of beryllium of 0.1% to0.5% and content of nickel from 0.5% to 2% for molds, in particular forproduction of broad side plates for thin slab continuous casting molds.2. Use of a hardenable copper alloy according to claim 1 for productionof broad side plates for thin slab continuous casting molds with castingspeeds of at least 2 to 6 m/min.
 3. Use of a hardenable copper alloyaccording to claim 1 or 2 with alloying components of 0.1% to 0.5%beryllium and 0.5% to 2% nickel which, with a copper component amountsto at least 99.5%.
 4. Use of a hardenable copper alloy according to oneor more of claims 1 through 3 which, except the alloying components ofberyllium, nickel and copper, contain maximum 0.5% of impurities.